CDN for Video Streaming: Architecture and Best Practices

Content Delivery Networks are essential infrastructure for video streaming at scale. CDNs distribute content globally, reduce latency, and enable platforms to handle millions of concurrent viewers without overwhelming origin servers.

CDN Architecture Fundamentals

A CDN is a geographically distributed network of servers that work together to deliver content quickly and reliably.

Core Components

Origin Server: The source of truth hosting original video content, manifests (m3u8/mpd), and metadata. May be your own infrastructure or cloud storage.

Edge Servers: Caching servers deployed in data centers worldwide, serving content to nearby users. Also called edge nodes or PoPs (Points of Presence).

PoPs (Points of Presence): Physical data center locations containing edge servers. Major CDNs operate 200+ PoPs globally.

Routing Layer: DNS-based or anycast routing that directs user requests to the optimal edge server based on geography, load, and health.

Request Flow

1. User requests video segment from CDN URL

2. DNS or anycast routes request to nearest PoP

3. Edge server checks local cache for content

4. Cache hit: Content served immediately (fast path)

5. Cache miss: Edge fetches from origin, caches locally, serves to user

Edge Caching Strategies

Caching behavior differs significantly between VOD and live streaming.

VOD (Video on Demand) Caching

Long TTLs: VOD content does not change, so cache for hours or days.

Popularity-Based Caching: Pre-cache popular content at edges. Let cold (rarely accessed) content be fetched on-demand.

Chunk-Level Caching: Cache individual video segments independently. Popular segments stay cached longer.

Content TypeRecommended TTLPre-caching Popular VOD24-72 hoursYes Long-tail VOD1-4 hoursNo Thumbnails24+ hoursYes Manifests5-60 minutesNo

Live Streaming Caching

Short TTLs: Live segments must be fresh. TTL typically matches segment duration.

Just-in-Time Caching: Segments cached as they are generated at origin.

Manifest Refresh: Live manifests update frequently (every segment). Use short TTL or no-cache with revalidation.

Content TypeRecommended TTLNotes Live segmentsSegment duration (2-10s)Longer for replay Live manifest1-2 secondsOr no-cache DVR segments1-4 hoursOlder segments

Geographic Distribution

Strategic edge server placement minimizes latency for global audiences.

Latency Impact

Round-trip time significantly affects video startup and quality:

Same continent: 20-50ms
Cross-continent: 100-200ms
Intercontinental without CDN: 200-400ms

PoP Placement Strategy

Tier 1 Markets: Major metro areas with highest user density. Multiple PoPs for redundancy.

Tier 2 Markets: Secondary cities and regional hubs. Single PoP serving surrounding area.

ISP Peering: Direct connections to major ISPs reduce last-mile latency.

Example: Global Live Event

For a major sporting event with global audience:

Origin server in US East
50+ edge PoPs worldwide activated
Users served from nearest PoP
Effective latency: Less than 50ms to edge vs 200ms+ to origin

Origin Shielding

Origin shielding protects your origin server from being overwhelmed by edge requests.

How Shielding Works

Without shielding: Every edge PoP fetches independently from origin for cache misses.

With shielding: Edge servers fetch from regional shield servers, which then fetch from origin.

Result: Single origin request can serve multiple edge PoPs through the shield.

Shielding Benefits

Load Reduction: 90%+ reduction in origin requests.

DDoS Protection: Origin IP hidden behind shield layer.

Cost Savings: Reduced origin bandwidth and compute.

Consistency: Shield ensures all edges serve identical content.

Shield Placement

Place shield servers in regions with highest edge traffic:

North America shield for US/Canada PoPs
European shield for EU PoPs
Asia-Pacific shield for APAC PoPs

Scaling for Traffic Spikes

Live events can see 10-100x normal traffic in seconds.

Pre-Event Scaling

Capacity Planning: Estimate peak concurrent viewers. Add buffer.

Edge Pre-warming: Optionally push content to edges before event.

Origin Scaling: Ensure origin can handle shield requests during ramp-up.

Real-Time Scaling

Auto-scaling: CDNs automatically add edge capacity based on demand.

Load Balancing: Distribute traffic across multiple servers within each PoP.

Overflow Routing: Redirect traffic to less-loaded PoPs if primary is saturated.

Traffic Spike Handling

Traffic IncreaseCDN ResponseOrigin Impact 2-5xAutomatic scalingMinimal 5-20xMulti-PoP distributionModerate (if shielded) 20-100xRegional overflow, rate limitingSignificant (prepare ahead)

CDN Selection Criteria

Technical Factors

PoP Coverage: Number and location of edge servers. More PoPs means lower global latency.

Video Features: Native HLS/DASH support, token authentication, DRM integration.

Performance: Consistent low latency, high cache hit ratios, fast purge.

Reliability: SLA guarantees, redundancy, failover capabilities.

Business Factors

Pricing Model: Per-GB, committed bandwidth, or hybrid. Consider your traffic patterns.

Support: 24/7 support availability, dedicated account management.

Integration: APIs, dashboards, real-time analytics.

Major CDN Providers

Cloudflare: Global network, competitive pricing, strong security features.

AWS CloudFront: Deep AWS integration, flexible origin options, Lambda@Edge.

Fastly: Real-time purge (less than 200ms), edge compute (Compute@Edge), developer-friendly.

Akamai: Largest network, enterprise focus, comprehensive video solutions.

Bunny CDN: Budget-friendly, good performance, simple pricing.

Best Practices

Caching Configuration

Set appropriate Cache-Control headers at origin
Use versioned URLs for cache busting when needed
Implement stale-while-revalidate for improved hit rates
Configure proper Vary headers for multi-codec delivery

Performance Optimization

Enable HTTP/2 or HTTP/3 for multiplexed connections
Use persistent connections between edge and shield/origin
Compress manifests and metadata (gzip/brotli)
Consider edge compute for dynamic manifest manipulation

Monitoring and Alerting

Track cache hit ratio (target: greater than 95% for VOD)
Monitor origin offload percentage
Alert on latency percentile increases (p95, p99)
Watch for error rate spikes (5xx responses)

Security

Enable HTTPS everywhere (TLS 1.3)
Implement token authentication for premium content
Configure rate limiting to prevent abuse
Use WAF rules for additional protection

Conclusion

CDNs are critical infrastructure for video streaming at scale. Key priorities when implementing CDN for video:

1. Global Coverage: Deploy edges close to your audience

2. Smart Caching: Configure TTLs appropriate for content type

3. Origin Protection: Implement shielding to reduce origin load

4. Scalability: Plan for traffic spikes with auto-scaling and overflow

Properly configured CDN infrastructure enables platforms to deliver high-quality video to millions of viewers simultaneously while controlling costs and maintaining reliability.

Platforms like dcast.tv include integrated CDN delivery with automatic edge caching, origin shielding, and global distribution, handling the complexity of video delivery infrastructure so creators can focus on content.